The present invention relates to an optical recording medium which permits information to be written thereinto and read thereoutof by means of laser light and, more particularly, to a medium comprising a substrate having a dye-containing recording layer on at least one side.
Various kinds of optical recording media have been developed heretofore. There is one particular type of media which permits instant laser recording without processing and, for this reason, it is sometimes referred to as direct-read-after-write (DRAW) media. DRAW media are disclosed in a large number of patents issued up to now. Recording materials used in DRAW media are available in a wide range, from inorganic to organic substances. Among them, organic dyes have been considered due to their potential advantages over inorganic substances, such as Te-alloys in regard to recording sensitivity, chemical stability and fabrication latitude.
Media using organic dyes are accessible in various forms and may generally be classified into two types, i.e., dye film type and dye-in-polymer type. Dye film type media can be produced on a substrate by means of vapor deposition of a dye. U.S. Pat. No. 4,023,185, issued May 10, 1977, to Bloom, Bartolini and Bell of RCA Corporation describes the use of 4-phenylazo-1-naphthylamine to form a dye film as a recording layer. The medium having the dye film is inapplicable to semiconductor layer recording, because it does not show a sufficient absorption in the semiconductor laser wavelengths (.about.800 nm). U.S. Pat. No. 4,298,975, issued Nov. 3, 1981, to van der Veen, Kivits and de Bont of U.S. Philips Corporation discloses the use of phthalocyanine compounds as a dye. Phthalocyanine compounds, especially vanadyl phthalocyanine, are even worse than Te-alloys with respect to recording sensitivity for semiconductor lasers, although exhibiting a relatively large absorption in the near infrared range. Meanwhile, dye-in-polymer type media can be prepared by means of coating of a solution containing dye dissolved in an organic polymer with a solvent. A dye-in-polymer type medium may be formed by the use of polyester yellow as a dye and polyvinyl acetate as an organic polymer, as described in Japanese Patent Laid-Open Publication No. 161690/1980, for example. The medium, however, cannot serve as a medium for recording apparatus of the type which uses semiconductor lasers, because polyester yellow shows weak absorption in the semiconductor laser wavelength range.